Method of and apparatus for controlling a variable pitch steering propeller

ABSTRACT

A variable pitch steering propeller for a ship is controlled by continuously monitoring the power supplied to the propeller to drive it and producing a signal indicative thereof, generating a reference signal indicative of a desired propeller power output, comparing the two signals and producing a control signal representative of the difference between the actual power signal and the reference signal and adjusting the pitch of the propeller in accordance with the control signal.

United States Patent Olof Rolf Gosta Mogren;

Tord Birger Svensson, both of Kristinehamn, Sweden Apr. 30, I969Inventors Appl. No. Filed METHOD OF AND APPARATUS FOR CONTROLLING AVARIABLE PITCH STEERING PROPELLER 8 Claims, 1 Drawing Fig.

Primary ExaminerEverette A. Powell, Jr. Attorney-Brumbaugh, Graves,Donohue & Raymond ABSTRACT: A variable pitch steering propeller for aship is controlled by continuously monitoring the power supplied to thepropeller to drive it and producing a signal indicative thereof,generating a reference signal indicative of a desired U.S.Cl propellerpower output, comparing the two signals and 4l5/35,4l6/35 producing acontrol signal representative of the difference Int. Cl B63h 25/42between the actual power signal and the reference signal and Field ofSearch 416/35, 43, adjusting the pitch of the propeller in accordancewith the 31, 38, 157 control signal.

2 ggf CONTROLLER 5 25amoron START CONTROL 29 29a 196158,; COMPARATOR 9moron v HYDRAULIC so PRESSURE l souncs i 5 23 2/ 25 1 l 1='r1: P

1 11 OSIT o 3 l MONITORI N PATENIEUJUHZSIQYI 3,589,830

POWER SUPPLY CONTROLLER MOTOR START CONTROL POWER MONITOR COMPARATORCOMPARATOR HYDRAULIC PRESSURE SOURCE PITCH POSITION I5 MONITOR theirATTORNEYS METHOD OF AND APPARATUS FOR CONTROLLING A VARIABLE PITCIISTEERING PROPELLER BACKGROUND OF THE INVENTION This invention relates toa methodof and an apparatus for controlling a variable pitch propeller,and particularly for controlling a steering propeller located in atunnel extending athwart the hull of a ship.

Steering propeller installations of the kind referred to above, such asthat described and shown in, for-example, US. Pat. No. 3,002,486,provide a turning effect on the ship by the action of a steeringpropeller that drives a stream of water through a tunnel athwart theship. The steering propeller is usually driven by an electric motor,although other sources of driving power may be used. The blades of thesteering propeller are mounted to a hub in a manner such that theirpitch may be adjusted, generaLly by means of a hydraulic adjustingmechanism comprising a hydraulic cylinder and piston arranged in the huband equipment for providing and controlling the delivery of a hydraulicfluid to the cylinder. The hydraulic adjusting mechanism is usuallyarranged for remote control from the bridge of the ship. By adjustmentof the blades, the steering propeller can be set to different pitches,from maximum pitch in one direction to maximum pitch in the oppositedirection, without reversing the direction of rotation of the propeller.

A steering propeller, especially one located in a tunnel athwart thehull, is often operated under conditions which vary considerably as aresult of such changing factors as the direction of movement of the shiprelative to the water and is also subject to intrusion of foreignobjects, e.g., ice or debris into the tunnel which affect operation.Because steering propeller installations known heretofore are, inprinciple, arranged for direct setting of the propeller pitch from thebridge, there is always a risk that the pitch may be set to valueswhich, under certain conditions of operation, will overload the drivingmotor of the steering propeller or means that the propeller installationmay not be utilized in the most efficient way. An overload may causemotor breakdown and consequent lost steering ability.

SUMMARY OF THE INVENTION There is provided, in accordance with theinvention, a

method of and an apparatus for controlling the steering effect of acontrollable pitch steering propeller by which any desired steeringeffect is obtained under all operating conditions, without any risk thatthe driving motor of the steering propeller will be overloaded.

The energy requirement for powering a steering propeller is determinedby the pitch and the speed of the propeller as well as by the operatingconditions, for example, the speed and direction of the ship relative tothe water and the presence of obstacles such as ice or debris in thetunnel. One aspect of the invention is a solution for the problem of howto limit the power consumption of the steering propeller to values thatdo not exceed the safe-operating power of the driving motor and thatprovide for the intended steering effect.

The method, according to the invention, involves, basically, the controlof the pitch-setting mechanism of the propeller blades in accordancewith a signal from a control device representing the difference between,on one hand, a reference value signal indicative of a desired output ofthe driving power of the steering propeller and, on the other hand,

an actual load" signal indicative of the actual power output of thedriving motor or engine.

Apparatus according to the invention comprises a manually adjustablecontroller that generates a reference value signal the load-monitoringdevice and produces from then a control signal which is used to controlthe hydraulic pitch-setting mechanism of the propeller blades in such away that the propeller blades will be set to a pitch corresponding tothe desired output.

The transverse thrust for steering a ship, which is produced by thesteering propeller, is mainly determined by the power consumed by thesteering propeller. It is therefore advantageous to control this powerdirectly within the proper limits allowed for the motor. When thesteering propeller is driven by an electric AC motor, as it is in mostcases, the supply voltage and operating speed will be essentiallyconstant and the motor output load-sensing device may therefore comprisea current transformer connected in the power supply line to the motor,since the motor power output under those conditions is proportional tothe current.

DESCRIPTION OF THE DRAWINGS For a better understanding of the invention,reference may be made to the following description of an exemplaryembodiment of the method and apparatus, taken in conjunction with theaccompanying drawing, which is a schematic illustration of theembodiment of the apparatus.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT The embodiment of the controlsystem, according to the invention, is depicted in the drawing inassociation with a marine steering system that comprises a propeller Imounted in a transverse tunnel through the hull of a ship (not shown)and driven by an electric motor 9 through an appropriate gear system 7.The blades 5 of the propeller are mounted on a hub 3 in such a mannerasto be rotatable about radial axes, relative to the hub, to provide pitchsettings ranging from a maximum pitch to provide propulsion in onedirection to a maximum pitch providing propulsion in the otherdirection. The pitch of the propeller blades 5 is altered and ismaintained in any selected position by a hydraulic pitch-settingmechanism 11 composed of a hydraulic cylinder 13 having a double-actingpiston 15 and supplied from a source of hydraulic pressure 21 through acontrollable valve 17, such as a solenoid valve. The hydraulic pressuresource 21 may be connected, by way of the hydraulic lines 23 to thecylinder 13 selectively to deliver pressure to either side of the piston15 in accordance with the position of the valve. If the valve 17 is setso that hydraulic pressure is delivered to the left side of the piston,the pitch ofthe propeller blades 5 is changed in one direction, ansimilarly the delivery of hydraulic pressure to the right side of thepiston alters the propeller pitch in the other direction. In eithercase, the fluid pressure is bled from the cylinder through the nonactivesupply conduit 23. Various specific designs for the hydraulicpitch-setting mechanism and the coupling of the mechanism to thepropeller blades have been proposed and used, and the control system,according to the invention, may be used with a variety of differentspecific designs.

The activation of the steering system and the control of its operationis preferably accomplished from the bridge of the ship, and to that'end, a controller 25 is provided on the bridge. The controller includesa start-stop switch 26, or any other suitable medium for starting andstopping the motor 9 and activating the control system when it isdesired to use the steering system to maneuver the ship. The startingapparatus is operated at the bridge and initiates the starting sequenceprovided by the motor start control 28, which may be any suitable formof starting circuitry, usually relay circuitry, for starting and runningthe motor 9 up to speed. As will be described below, the steeringcontrol system ensures that the propeller blades are in a neutral (zeropitch) position during motor starting, so that the load on the electricdrive motor is at a minimum until the motor has reached operating speed.

The controller 25 is provided with a suitable device for generating avariable reference signal representing a desired which the output is acontinuously variable alternating current' signal. At the controller 25on the bridge, a control lever is adjusted by the operator to select anydesired propeller loading over a range corresponding to a maximumpropeller power output in one direction to a maximum power output in theother direction (i.e., full starboard or full port steering effect).Thus, once the steering system is activated, movement of the lever 27 toany position results in the development of a corresponding referencesignal on the conductor 25a, which in turn controls the desired steeringpropeller output and direction. However, an appropriate interlockbetween the motor start control and the controller prevents operation ofthe control system until the motor 9 has reached operating speed. Themaximum reference signal generated by the controller 25, for eitherpitch direction, is limited to a value that provides a propeller poweroutput that is not in excess of a safe-operating load on the motor 9; Aswill be apparent below, the controller thus establishes a maximum powerload on the motor and prevents overloading and the consequentpossibility of damage to or burnout of the motor.

The power output of the motor is continuously monitored and a signalproduced that is compared with the reference signal set on thecontroller 25. When an electric motor of the type operating at aconstant voltage and constant speed is used, i.e., a synchronous motor,the power monitor 33 may comprise a current amplifier receiving an ACsignal from a current transformer (not shown) in the line (s) betweenthe power supply and motor armature. The power monitor 33 provides acontinuous signal indicative of the actual power output of the motor,such signal being appropriately termed an actual load" signal. Theactual load signal from the power monitor 33 and the reference signalfrom the controller 25 are compared in a comparator 29, which may beofany of a 'number of electrical or electronic devices that are, per se,well known in the art, such as voltage, phase or polarity detectingrelay circuits. The comparator 2 detects any difference between theactual load signal and the reference signal and produces an outputsignal on the conductor 30, representative of an error or correctionvalue, and the correction signal is used to operate the solenoid valve17 in an appropriate manner to deliver hydraulic pressure to thehydraulic cylinder to alter the pitch in the manner required to matchthe actual propeller output with the preset control value selected atthe controller 25. For convenience, the actual load signal from thepower monitor 33 may be referred to as the first signal, the referencesignal from the controller 25 may be referred to as the second signal,and the correction signal from the comparator 29 may be referred to asthe third signal.

For example, if it is desired to establish a maximum steering effect inthe starboard direction, the controller operating lever 27, which is amanually operable control located on the bridge of the ship, is moved toan indicated position, such that the controller generates a referencesignal corresponding to the maximum output of the propeller to providepropulsion in the starboard direction. Assuming that the motor has beenstarted up and is running at speed, the reference signal on theconductor 25a and the signal from the power monitor 33 (representing theactual power being delivered by the motor) are compared in thecomparator. Inasmuch as the motor is then running at approximately ano-load, or minimum load, condition with the propeller pitch at neutral,an error signal is generated and is applied to the solenoid valve 17 toshift the valve to a position providing delivery of hydraulic pressureto the part of the cylinder appropriate to drive the piston in adirection to adjust the blade pitch for starboard thrust. As thepropeller blade pitch is changed, the load on the motor increases andthe actual load signal from the monitor 33 similarly increases; but aslong as there is an error signal at the comparator output, the pitch ofthe propeller will continue to increase. When the actual load signalattains a value matching the reference signal, which means that themotor load corresponds to the desired propulsion output of thepropeller, the error signal decreases to a minimum value and thesolenoid valve is shifted to a position shutting off the hydraulic line,thereby leaving the propeller pitch set to the proper position.

if there should be a change in the operating conditions in the tunnel,such as might be caused by the intrusion of ice or debris, which wouldincrease the motor above the maximum safe-operating load at the existingpropeller pitch, an increased error signal is generated in thecomparator and is supplied to the solenoid valve to reduce the propellerpitch until there is again a balance between the motor output and thepresent propeller output. When a balanced condition is againestablished, the error signal again drops to its minimum value, and thepropeller blades remain set in the new, readjusted pitch position.

Accordingly, the control system, according to the invention, providesfor the maintenance of a preestablished propeller power outputregardless of the conditions'under which the propeller is operating andin accordance with any change in the conditions in the steeringpropeller tunnel. The propeller blade pitch will be alteredappropriately by the control system without manual correction by theoperator to maintain a desired propulsion output in a given direction,but in no case placing a.demand on the motor in excess of asafe-operating load.

As a further safety feature, the apparatus of the invention alsoincludes a system for ensuring that the motor cannot be started when thepropeller blades are in any position other than a neutral pitchposition, thus providing for starting the motor under a minimum loadcondition. in particular, the apparatus includes a pitch positionmonitor 35, which may be any suitable electromechanical or electricaldevice. Inasmuch as the piston occupies a position in the cylinder thatis directly related to the pitch position of the propeller blades, theposition of the piston in the cylinder provides a convenient indicatorand mechanical arrangement for monitoring the pitch position. The pitchposition monitor 35 may be arranged to be under the control of thecontroller 25 so that an any time the controller is operated to startthe motor the pitch position monitor is also energized. The monitor ispreferably arranged to provide an interlock signal, on a conductor 36,which renders the motor start control 28 inoperative. If the propellerblades are in any position other than a neutral position, the motorstart control is thus overridden. in the meantime, the pitch positionmonitor 35 also generates a signal indicative of the propeller pitchposition, and that signal is supplied to a comparator 29a, which mayactually be a subcomponent of the main comparator 29.

The controller 25 is arranged automatically to provide, at such time asthe motor power is turned off, a reference signal and to conduct thesignal to the comparator 29a. Such reference signal is representative ofthe desired pitch, usually neutral position, of the propeller bladesduring motor start-up. The comparator 29a compares that reference signalwith the pitch position monitor signal and produces an error signalwhich controls the operation of the solenoid valve 17. The referencesignal is established at a value sufficient to produce in the comparatoran error signal for any position of the propeller blades other than thedesired position of the blades during motor starting. The error signalis connected to the solenoid valve over the conductor 31 and actuatesthe valve appropriately to provide hydraulic pressure delivery to thecylinder in a manner such as to actuate the hydraulic mechanism and movethe propeller blades to the starting position.

Preferably, the controller is designed to carry out the starting, orzero pitch, adjustment automatically whenever the steering system isturned off. This can be accomplished in a number of ways, such as byproviding a timer or latching relay to maintain the pitch positionmonitor and hydraulic pressure equipment in operation for either asufiicient time tocomplete a centering operation or until such time asthe centering operation. is completed with automatic shut-off. In thesimplest case, the comparator 29a may be made operable only when thestart-stop switch 26 is in the off position, during which time thecomparator 29 is inoperative. Accordingly, the propeller blades aremoved to a neutral pitch position when p the steering system is shutdown and are therefore in a position for starting up when'the steeringsystem is activated again.

' The embodiment of the invention described above is intended to bemerely exemplary, and those skilled in the art will be able to makenumerous variations and modifications of it without. departing from thespirit and scope of the invention. Thus, the particular units describedabove may be replaced by equivalent units of different types, butoperating in substantially the same manner. Moreover, the system may beadapted to propeller power sources of other types, such as a directcurrent motor or a diesel engine, by providing an appropriate type ofunit to monitor and produce a signal indicative of the output power.

We claim:

1. A method of controlling the load on an electric motor used to drive avariable pitch steering propeller of a ship comprising:

generating a first electrical signal indicative of the current flow intothe electric motor and therefore indicative of the actual load on themotor;

generating a second electrical signal indicative of a load for theelectric motor selected by the operator, this load not exceeding themaximum desirable load for the motor;

comparing the first and second signals and generating a third electricalsignal indicative of the difference therebetwee'n, the third signalbeing indicative of the difference, if any, between the actual load andthe selected load; and using the third signal to control the pitch ofthe steering propeller whereby the actual load on the motor is adju stedand made substantially equal to the selected load.

2. The method according to claim lwherein the step of generating thefirst signal comprises passing at least a portion of the current flowinginto the motor through a current generator.

3. The method according to claim I wherein the step of generating thesecond signal includes the manipulation of a manually operable controlon the bridge of the ship.

4. A ship having a steering propeller of variable pitch disposed withina tunnel extending athwart the hull of the ship and an electric motorfor driving the steering propeller wherein the improvement comprises, ameans for generating a first electrical signal indicative of the currentflow into the motor, a means for generating a second-electrical signalindicative of a selected load for the motor, a comparitor means arrangedto receive said first and second electrical signals for generating athird electrical signal indicative of the difference .therebetween, andmeans for adjusting the pitch of the propeller in response to the thirdsignal.

5. The apparatus of claim 4 wherein the means for generating the firstelectrical signal comprises a current generator arranged so that atleast a portion of the current supplied to the electric motor flowsthrough it.

6. The apparatus of claim 5 wherein the means for adjusting the pitch ofthe propeller includes a hydraulic valve the position of which isvariable in response to the third signal.

7. The apparatus of claim 4 wherein the pitch of the blades of thepropeller is reversible whereby the direction. of the transverse thrustfor steering the ship produced by the propeller can be reversed withoutreversing the direction of rotation of the propeller, said improvementfurther comprising means for causing said propeller to assume a positionof neutral pitch when the steering system is turned off.

8. The apparatus of claim 4 wherein said electric motor is a synchronousmotor.

1. A method of controlling the load on an electric motor used to drive avariable pitch steering propeller of a ship comprising: generating afirst electrical signal indicative of the current flow into the electricmotor and therefore indicative of the actual load on the motor;generating a second electrical signal indicative of a load for theelectric motor selected by the operator, this load not exceeding themaximum desirable load for the motor; comparing the first and secondsignals and generating a third electrical signal indicative of thedifference therebetween, the third signal being indicative of thedifference, if any, between the actual load and the selected load; andusing the third signal to control the pitch of the steering propellerwhereby the actual load on the motor is adjusted and made substantiallyequal to the selected load.
 2. The method according to claim 1 whereinthe step of generating the first signal comprises passing at least apOrtion of the current flowing into the motor through a currentgenerator.
 3. The method according to claim 1 wherein the step ofgenerating the second signal includes the manipulation of a manuallyoperable control on the bridge of the ship.
 4. A ship having a steeringpropeller of variable pitch disposed within a tunnel extending athwartthe hull of the ship and an electric motor for driving the steeringpropeller wherein the improvement comprises, a means for generating afirst electrical signal indicative of the current flow into the motor, ameans for generating a second electrical signal indicative of a selectedload for the motor, a comparitor means arranged to receive said firstand second electrical signals for generating a third electrical signalindicative of the difference therebetween, and means for adjusting thepitch of the propeller in response to the third signal.
 5. The apparatusof claim 4 wherein the means for generating the first electrical signalcomprises a current generator arranged so that at least a portion of thecurrent supplied to the electric motor flows through it.
 6. Theapparatus of claim 5 wherein the means for adjusting the pitch of thepropeller includes a hydraulic valve the position of which is variablein response to the third signal.
 7. The apparatus of claim 4 wherein thepitch of the blades of the propeller is reversible whereby the directionof the transverse thrust for steering the ship produced by the propellercan be reversed without reversing the direction of rotation of thepropeller, said improvement further comprising means for causing saidpropeller to assume a position of neutral pitch when the steering systemis turned off.
 8. The apparatus of claim 4 wherein said electric motoris a synchronous motor.